Inertia latch systems are known in the art for two-door passenger vehicles wherein the seat back may be moved forwardly to accommodate passenger entrance and exit without the need for actuating any manual release lever, subject however to an inertia element locking the seat back against forward movement in response to accident or emergency deceleration thereby preventing the seat back and any rear passenger from inertia propulsion against the driver or front seat occupant.
The inertia element in such systems is preferably positioned in a latching attitude in response to seat back return to its normal position, subject to being freed for gravity actuation to a release position by initial forward seat back movement, but also being subject to retention in a latching attitude by inertia incident to a predetermined rate of deceleration such as encountered in an accident or emergency braking.
Examples of such prior art systems employ an inertia element pivotally mounted on the seat back with a forward projection held in a latching attitude relative to an abutment stop mounted on the seat until initial forward movement of the seat back permits gravity to actuate the inertia element to a nonlatching attitude. Inertia forces on the center of gravity in a horizontal direction are effective to hold the inertia element in latching attitude under predetermined deceleration values. Such systems are shown in U.S. Pat. Nos. 4,165,128 issued Aug. 21, 1979; 4,223,946 issued Sept. 23, 1980; 4,438,974 issued Mar. 27, 1984; 4,469,375 issued Sept. 4, 1984; and 4,619,031 issued Oct. 28, 1986.
In some systems, an inertia element is mounted on the seat with a projection adapted to engage an element mounted on the seat back, for example, as disclosed in U.S. Pat. No. 4,402,747 issued Sept. 6, 1983; in some cases, composite elements are employed for the inertia latch as in U.S. Pat. No. 4,429,919 issued Feb. 7, 1984; and in some cases spring elements have been employed to supplement inertia effects on the inertia element as in U.S. Pat. No. 4,358,155 issued Nov. 9, 1982 and 4,366,984 issued Jan. 4, 1983.
In general, it is essential in the type of inertia latch under consideration, to provide sufficient lost motion to accommodate gravity displacement of the inertia element to a nonlatching clearance during initial forward tilting of the seat back while minimizing such lost motion, typically in the order of 7.degree. to 8.degree., relative to effective latch engagement to arrest forward seat back tilting when required by sudden deceleration. A reduction in such lost motion for latch engagement is a recognized objective. It is also important that release of the inertia latch by gravity be effective when the car is parked on relatively steep grades and that the predominate effect of inertia in overcoming the gravity moment be reliable in all cases of deceleration exceeding a predetermined limit.